Apparatus and method for web cooling in a vacum coating chamber

ABSTRACT

A chill drum ( 14′ ) is modified to improve heat transfert between the drum and a flexible web substrate ( 20 ) disposed around the drum. The drum surface ( 22 ) contains a series of passages ( 44 ) and distribution holes ( 46 ). A working gas is injected into these passages and flows out of the distribution holes into the space between the web and drum. A cover ( 32 ) prevents working gas from escaping from frum passages in the area not covered by the web, and supplies the working gas to the passages at the drum cover. Once gas is in the passages, leakage only occurs from the edges of the web. The pressure in the passages remains essentially constant around the drum, producing uniform elevated pressures under the entire web. Elevated pressure behind the web significantly improves overall heat transfert, thereby allowing higher deposition rates and other process advantages.

BACKGROUND

[0001] This invention relates to a device and method for improving heattransfer between a web and a chill drum in a vacuum chamber.

[0002] Many vacuum deposition processes involving flexible websubstrates are accomplished with the web disposed around a rotatingchilled drum. In these systems, deposition sources are arrayed aroundthe drum and continuously deposit coatings onto the moving web. Alimiting parameter of these deposition processes is the heat imparted tothe web during the coating process. If the heat applied by the processexceeds maximum web parameters, the web wrinkles or is otherwisedamaged. Many products today are either expensive or are not producedbecause of low deposition rates dictated by insufficient web heattransfer.

[0003] Heat removal from a web to a chilled drum is primarily limited bythe interface between the web and drum. In this interface, heat istransferred by three modes. One mode is conduction between the twosurfaces. Typical polymer webs are not smooth at the micron level. Theyare made intentionally rough to allow the film to be wound on a spool.While improving ease of handling, this surface roughness greatly reducesthe actual contact between the web and the drum. Lack of contact in turnlimits the heat transfer by conduction to less than 5% of the total heattransfer. A second heat transfer mode is radiation. While alsocontributing to heat removal, heat removed by this mode is limited bythe relatively small temperature difference possible between the web anddrum.

[0004] The third and largest contributor to heat transfer between theweb and drum is molecular conduction. This mode occurs when moleculestrapped between the web and drum transfer heat between the two surfaces.Commonly water vapor is present in polymer substrate films and devolvesfrom the substrate during the deposition process. A portion of thiswater vapor is trapped between the web and drum and provides a mediumfor molecular conduction heat transfer. Important factors determiningthe rate of molecular conduction heat transfer include: the temperatureof the web and drum, the web and drum materials, the type of gas, andthe pressure of the gas. Variations to web and drum temperatures andmaterials are limited by materials properties; however, a significantopportunity for improvements in heat transfer resides with the type ofgas and the pressure of the gas. If these variables can be optimized,the heat load into the web can be increased without damage to the web.Because the pressure can be varied by orders of magnitude, it offers thebest lever for dramatic heat transfer improvement.

[0005] Several prior-art devices have attempted to improve theweb-to-drum heat transfer by elevating the pressure between the web anddrum:

[0006] U.S. Pat. No. 3,414,048 (Rall) discloses a drum with built innormally closed valves. Web in contact with the drum forces open thevalves, allowing gas to flow into the gap between the web and drum. Thisapparatus is complicated with many parts to stick or fail. Also a thinpolymer web may fail to exert sufficient pressure on the valve to openthem. Other limitations of this approach include hot spots on the web(the valves are not cooled) and non-uniformity of web cooling.

[0007] U.S. Pat. No. 5,076,203 (Vaidya) discloses apparatus to increasethe pressure behind the web by blowing gas into the gap with a nozzlearrangement. Another method to increase pressure employs a porous metalnon-rotating section through which gas is distributed. An enclosurearound the web and drum at the entrance point of the web is shown as ameans to limit the increase in chamber pressure as gas is urged into thegap. While informative, several faults limit the utility of this deviceand method:

[0008] No means is described to continually trap working gas behind theweb in a rotating drum configuration. Due to the minute quantity of gastrapped as the drum rotates away from the nozzle area, most or alltrapped gas is lost before reaching the rewind side of the chamber.Therefore, the enclosure that is used to prevent gas from raising thesystem pressure only envelopes the unwind drum side. This indicates thesmall amount of gas actually urged into the web. High pressures wouldresult in large gas loads on the chamber vacuum system.

[0009] No means is disclosed to bring a working gas into a porousmaterial where the porous material is applied to the surface of arotating drum.

[0010] No means is disclosed to alter the pressure effectively acrossthe width of the web for the purpose of controlling web heat transferand conveyance parameters. Distribution of gas in the porous surfaces isacross the width of the drum.

[0011] In U.S. Pat. No. 5,395,647 (Krug), a vapor such as water iscondensed onto the web prior to contact with the chill drum. Whilerecognizing the need to improve heat transfer between the web and drum,this method lacks practicality for most deposition processes. The use ofliquid water creates an undesirably large gas load on the pumpingsystem, and uniformly dispensing of water vapor in vacuum is difficult.While clean and of a suitable vapor pressure, water vapor is detrimentalto the formation of many desirable films. If a low vapor pressure fluidother than water is used, the web becomes contaminated with thesubstance.

SUMMARY

[0012] By way of general introduction, the web coating apparatusdescribed below includes a rotatable drum that carries a web past acoating deposition station in a vacuum chamber. Tension on the webpresses it against the drum over a first arc that includes the coatingregion of the apparatus, and the web is spaced from the drum in a secondarc disposed opposite the coating deposition station. The drum ischilled, as for example with conventional liquid cooling, and the drumis provided with an array of passages. These passages open out onto theweb support surface via exit portions that are continuously open. Asource of pressurized gas is coupled with these passages such thatpressurized gas is pumped via the passages and the exit portions intothe region between the web and the drum. This pressurized gas improvesheat transfer between the web and the drum.

[0013] In order to reduce undesired leakage of gas out of the passagesover the arc of the drum not covered by the web, a set of seals isprovided. These seals seal the exit portions of the passages in asealing region disposed opposite the coating deposition station. Theseseals can slide over the working surface of the drum (or alternatelythey can seal without contacting the working surface of the drum or theweb that is supported by the working surface of the drum), therebypreventing pressurized gas in the passageways from escaping out of thedrum into the region of the vacuum chamber adjacent the coatingdeposition station.

[0014] The foregoing paragraphs have been provided by way of generalintroduction, and they are not intended to narrow the scope of thefollowing claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a partially schematic plan view of a web coatingapparatus that incorporates a first preferred embodiment of thisinvention.

[0016]FIG. 2 is an enlarged view of selected portions of the apparatusof FIG. 1.

[0017]FIG. 3 is a perspective view of the drum and drum cover of theapparatus of FIGS. 1 and 2.

[0018]FIG. 4 is a cross-sectional view taken along line 4-4 of FIG. 2.

[0019]FIG. 5 is an exploded perspective view of an alternative drumsuitable for use in the apparatus of FIG. 1.

[0020]FIG. 6 is a fragmentary perspective view of another alternativedrum suitable for use with this invention.

[0021]FIG. 7 is a fragmentary cross-sectional view taken along line 7-7of FIG. 6.

[0022]FIG. 8 is a fragmentary plan view of a portion of the web supportsurface of another preferred embodiment.

[0023]FIG. 9 is a cross-sectional view taken along line 9-9 of FIG. 8.

[0024]FIG. 10 is a fragmentary plan view of a portion of the web supportsurface of yet another alternative embodiment of this invention.

[0025]FIG. 11 is a cross-sectional view taken along line 11-11 of FIG.10.

[0026]FIG. 12 is a schematic plan view of another preferred embodimentof this invention, in which seals seal against the web rather than theweb support surface of the drum.

[0027]FIG. 13 is a fragmentary schematic sectional view of anotherembodiment that provides gas at different pressures at different axiallyspaced regions of the web support surface.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

[0028] General Discussion

[0029] The present invention relates to an improved apparatus and methodfor increasing heat transfer between a flexible web and a chill drum ina vacuum chamber. This invention is particularly useful in improvingheat transfer in systems employing sources to deposit coatings onto theweb.

[0030] In one embodiment, a liquid-cooled drum is constructed with aseries passages around the drum perimeter with connecting tubes to thesurface of the web. These passages and tubes are proximal to the surfaceand are separate from the liquid cooling. A working gas is constantlyintroduced into the passages, raising the pressure inside the passages.The passages are of a sufficient size such that the conductance of thepassages far exceeds the leakage conductance from the edges of the web.For this reason, the passage pressure remains essentially constantthrough the entire length of the passage around the drum. Connectingtubes between the passages and drum surface allow gas to flow into thegap between the web and drum. The conductance limitation is the leakagefrom the edges of the web, and the pressure under the web thereforeequals passage pressure. For example, pressures of 10 Torr or greatercan be maintained between the web and drum while deposition zonepressures remain in the 5×10−4 Torr range. This is achieved because onlya minimal gas load is added to the deposition zone vacuum pumpingrequirements. This embodiment has several significant benefits, and itmakes feasible previously-unachievable deposition rates and processes.These benefits include the following:

[0031] The working gas is distributed to produce a uniform pressurearound the entire drum perimeter rather than only at one depositionzone. Effective heat removal is possible with systems employing multipledeposition sources installed around the drum (e.g. multiple sputtercathodes).

[0032] Pressure behind the web can optionally be controlled across thewidth of the web to optimize heat transfer, pumping loads and webeffects such as wrinkling.

[0033] With uniform gas distribution and pressure behind the web, localweb tension variations are mitigated. In typical chill drum depositionsystems, hot spots on the web cause local web expansion and loss ofoptimum thermal contact. Web wrinkling and other permanent damage canresult. The constant pressure delivered by the gas distribution networkdescribed below reduces hot spot occurrences.

[0034] The pumping load on the vacuum system is minimized. Whileconsiderable pressure can be maintained in the gap between the web anddrum, only a small gas load is added to the vacuum system. For example,With a typical ˜2 um gap between the web and drum due to web and/or drumroughness, a 10 Torr passage pressure leaks at only 0.002 Torr-liter/secinto the chamber.

[0035] The modifications required to a drum and web coater do not ruleout retrofit to an existing coater. Extensive pumping and windingchanges are not required. A standard construction chill drum can bemodified with a network of passages and holes. The sealing and gas inletcover can be retrofitted into an existing system, and the increased gasload on the vacuum pumps is minimal.

[0036] Rather than accept water vapor already in the web as the onlyheat transfer agent, a choice of gases can be used. In some cases aprocess gas can be used, e.g. the gas for sputter deposition. In thisexample the leakage from the web edges becomes part of the process gasdelivery system.

[0037] Specific Implementations

[0038] Turning now to the drawings, FIG. 1 shows a schematic plan viewof a web coating apparatus 10 that includes a vacuum chamber 12. Mountedinside the vacuum chamber 12 are a rotatable drum 14 and winding hubs16, 18. A web 20 to be coated is initially wound on the winding hub 16and is wrapped partially around the drum 14, supported by a web supportsurface 22 of the drum 14. The rotating drum 14 transports the web 20from the winding hub 16 past a coating deposition station 24 to thewinding hub 18. The coating deposition station 24 can include one ormore sources 26. In this example three sputter cathode magnetron sourcesare used, though more or fewer sources can be used of any suitable type.The region of the vacuum chamber 12 in the vicinity of the coatingdeposition station 24 will be referred to in the following descriptionas a coating region 28.

[0039] The web coating apparatus 10 also includes a sealed region 30that extends over an arc of the drum 14 that is angularly spaced fromthe coating region 28 and the coating deposition station 24. In thisexample, the sealed region 30 is bounded by a drum cover 32 thatincludes sliding seals 34 that slide against the web support surface 22immediately adjacent the two lines of contact between the web 20 and theweb support surface 22 as the web 20 approaches the drum 14 on one sideof the drum cover 32 and moves away from the drum 14 on the other sideof the drum cover 32.

[0040] In this example, a source 36 of pressurized gas is in fluidcommunication with the sealed region 30 bounded by the drum cover 32 andthe web support surface 22 of the drum 14. A pressure gauge 40 allowsthe pressure of gas in the region 30 to be monitored.

[0041]FIG. 2 provides an enlarged view that shows the relationshipbetween the drum cover 32, the sliding seals 34 and the drum 14. Asshown in FIG. 2, the drum 14 includes liquid cooling passages 42 throughwhich a cooling liquid is pumped by conventional means (not shown). Inthis example, the drum 14 also includes an array of passages 44. Eachpassage 44 extends circumferentially completely around the drum 14, andeach of the passages 44 is in fluid communication with the regionimmediately radially outwardly spaced from the web support surface 22via exit portions 46. In this embodiment, the exit portions 46 are eachshaped as a respective connecting tube that is constantly open betweenthe circumferential passage 44 and the exterior of the drum 14. Withthis arrangement, the drum cover 32 and the sliding seals 34 seal theexit portions 46 in the region of the web support surface 22 not coveredby the web 20. The web 20 itself seals the exit portions 46 over the arcof the web support surface 22 covered by the web 20.

[0042] In this embodiment, the pressurized gas from the source 36 passesinto the region 30 bounded by the drum cover 32 and creates a workingpressure P1. The pressure P1 is greater than the pressure P2 in thepassages 44, such that the pressurized gas continuously flows from thesource 36 through the region 30 and the exit portions 46 into thepassages 44. The drum cover 32 cooperates with the web 20 to contain thepressurized gas at an elevated pressure inside the passages 44. Workinggas is continually flowing into these passages via the region 30,thereby making up leakage loss and maintaining a substantially constantpressure P2 in all of the passages 44. In this way, gas pressure in thepassages 44 is maintained at a substantially uniform level at all pointsof contact between the web 22 and the drum 14.

[0043]FIG. 3 shows a perspective view of the drum 14 and the drum cover32. The exit portions 46 in the web support surface 22 are illustrated,as is one of the passages 44. Though not shown, a similar passage 44 ispositioned under each of the exit portions 46. In this example, thepassages 44 are circumferentially oriented and extend around the entireperimeter of the drum 14, and the exit portions 46 are shaped as smalltubes. As shown in FIG. 3, the sliding seals 34 at the edges of the drumcover 32 are in direct sliding contact with the web support surface 22of the drum 14. The spacing for the passages 44 and the exit portions 46is determined by the heat transfer requirements of the particularapplication. In this embodiment, the drum cover 32 acts as a manifoldcoupling the source of pressurized gas with the exit portions 46positioned in the sealed region 30 under the drum cover 32. In oneexample, the drum cover 30 and the associated manifold extend over theentire working width of the drum 14.

[0044]FIG. 4 provides an enlarged sectional view of two of the passages44 and two of the exit portions 46. The passages 44 ring the web supportsurface 22 and are of a depth and width such that the conductance lossthrough each passage 44 is small compared to the loss through the gapbetween the web 20 and the drum 14. In this way, the pressure in each ofthe passages 44 is maintained at a substantially constant level alongthe entire length of the passage 44 around the drum 14.

[0045] The exit portions 46 are small in comparison to the passages 44,and the exit portions 46 connect the passages 44 to the web supportsurface 22. The exit portions 46 are sized to present a sufficientconductance for gas to flow from the sealed region into the passages 44while minimizing the effects on the web 20 caused by interruptions inthe web support surface 22. The spacing of the passages 44 across thewidth of the drum 14 and the spacing of the exit portions 46 around theperimeter of the drum 14 are selected to create the desired pressuredistribution under the web 20. In one embodiment, the passages 44 andexit portions 46 are spaced to provide substantially constant pressurein the entire region between the web 20 and the drum 14. In anotherembodiment, the passages 44 and the exit portions 46 are spaced moreclosely in one portion of the web support surface 22 than another,axially-spaced portion of the web support surface 22. This designproduces elevated pressures of selected gasses in a selected pressuredistribution pattern under the web 20.

[0046] Of course, many variations are possible to the preferredembodiment described above. As shown in FIG. 5, the drum 14 can beprovided with passages 44′ that extend axially along the length of thedrum 14 rather than circumferentially as described above. In this casepressurized gas is introduced into the passages 44′ via a manifold 50 atone end of the drum 14. In this case, the drum cover 32 does not requireconnection to the source of pressurized gas.

[0047] As shown in FIG. 6, the exit portions 46′ may be shaped aselongated slits rather than the tubes described above. In general, thepassages 44, 44′ can be oriented at any desired angle rather than simplyat the circumferential and axial angles illustrated and discussed above,and the exit portions 46, 46′ can be shaped as any desired combinationof tubes, slits, and other elongated shapes extending partially or fullyalong the length of the associated passages.

[0048]FIGS. 8 and 9 relate to one method for forming the passages 44. Inthis example the drum 14 is first provided with a groove 52, and thisgroove 52 is then sealed with a strip 54 that includes indentations 56.These strips 54 and indentations 56 cooperate with the adjacent drum 14to form the passages 44 and the exit portions 46.

[0049] Another alternative arrangement is shown in FIGS. 10 and 11, inwhich the drum 14 is provided with a groove 56 that is closed with weldmaterial 58. This weld material 58 is then drilled to form the exitportions 46.

[0050]FIG. 12 relates to another alternative embodiment, in which seals34′ are positioned in close proximity to the web 20, which is in turn ispressed against the web support surface 22. In this embodiment, theseals 34′ are positioned over the web 20 rather than the drum 14. Asbefore, the seals 34′ define a sealed region 30′ that is separated fromthe coating region 28′. To avoid damage to the web surface, the seals34′ do not contact the web but are positioned in close proximity to theweb to limit the gas conductance between sealed region 30′ and coatingregion 28′. In this example, the sealed region 30′ includes the entirewinding zone, which is maintained at a sufficiently high pressure toforce gas via the exposed exit portions into the passages describedabove. Non-contacting seals of the type shown in FIG. 12 may be used inthe embodiment of FIG. 1 instead of the sliding seals 34 to reduceconductance between the drum 14 and the drum cover 32.

[0051]FIG. 13 shows another alternative that is closely related to theembodiment of FIGS. 1 and 2. In this case, the cover 32′ includes aseptum 60 that divides the region between the drum cover 32′ and thedrum 14 into two sealed regions 30″ and 30′″. In this case the gassource 26′ supplies pressurized gas to two pressure regulators 62, 64.The pressure regulator 62 is in fluid communication with the sealedregion 30″, and the pressure regulator 64 is in fluid communication withthe sealed region 30′″. The septum 60 forms a seal against the websupport surface 22, and in this way separate pressures P3, P4 aremaintained in the sealed regions 30″, 30′″ respectively. These differentpressures P3, P4 result in a desired pressure distribution along theaxial length of the drum 14 in the respective passages 44. Of course,three, four or more sealed regions and associated pressure regulatorscan be provided to achieve substantially any desired pressuredistribution across the width of the web.

[0052] The approach shown in FIG. 13 is useful in applications whereheat loads on the web are not uniform across the width of the web orwhere there are specific web transport requirements.

[0053] In another variation, the spacing of the passages 44, 44′ and theexit portions 46, 46′ may be varied to produce desired temperaturepatterns on the web.

[0054] The embodiments described above implement a method for coolingthe web 20. The drum 14 is rotated to transport the web 20 past thecoating deposition station 24. Pressurized gas is supplied to thepassages 44, 44′ and the continuously open exit portions 46, 46′ conductthis pressurized gas into the region between the web and the drum,thereby improving thermal contact between the web and the drum andcooling of the web. As the drum rotates, individual ones of the exitportions 46, 46′ move repeatedly between the coating region and thesealed region. When the exit portions 46, 46′ are in the coating region,the web 20 presses against the drum 14 adjacent the exit portions 46,46′ to reduce the leakage of pressurized gas into the coating region 28.When the exit portions 46, 46′ are aligned with the sealed region 30,the seals 34, 34′ minimize the undesired flow of pressurized gas out ofthe exit portions 46, 46′ into the coating region.

[0055] This invention can be adapted for use with the widest variety ofdrums, vacuum chambers, coating deposition stations, and sources ofpressurized gas. All of these elements can be modified widely asappropriate to fit the intended application. For example, the drum canbe provided with any desired axial length, and the axial length can besmaller or larger than the diameter of the drum. The angle over whichthe web is in contact with the drum can also be varied widely, includingsmall angles of wrap (less than 90°) as well as large angles of wrap(greater than 180°). This invention is not limited to any particularmaterial for the web. Steel, plastic or other materials can be used.

[0056] Also, the preferred embodiments described above work as intendedwhether the drum is rotated in the clockwise or the counter clockwisedirection. Many vacuum coating devices today include the ability to coatin both directions, and the preferred embodiments described above arewell suited for use in such devices.

[0057] By way of example only and without intending any limitation onthe following claims, the following preferred dimensions and materialshave been found suitable in one example. The passages 44 can be providedwith cross-sectional dimensions of 10 mm deep by 2 mm wide and acenter-to-center spacing along the axial length of the drum of 25 mm.The exit portions 46 can be circular in cross section with a diameter of0.3 mm and a length of 2 mm. The pressure P1 can be equal to 10 Torr,and the vacuum in the vacuum chamber 12 can be maintained at a pressureof 5×10−4 Torr. The drum 14 can be formed in the conventional manner ofcarbon steel with a hard, chrome-coated web support surface 22 polishedto a roughness average (Ra) of 0.2 micrometers.

[0058] As used herein, the term “set” is intended to indicate one ormore. The term “substantially prevent” as applied to leakage is intendedto indicate reduced leakage at an acceptably low level for the vacuumsystem being used. The term “source” as applied to pressurized gasincludes a source of a single gas at a single pressure as well as asource of one or more gasses at two or more pressures.

[0059] The embodiments described above will open new process avenuesbecause an elevated, controlled gas pressure is provided behind the webin a practical manner. The foregoing detailed description has discussedonly a few of the many forms that this invention can take. For thisreason, this detailed description is intended by way of illustration andnot limitation. It is only the following claims, including allequivalents, that are intended to define the scope of this invention.

1. A web coating apparatus comprising: a rotatable drum comprising a websupport surface and a plurality of passages, each passage comprising atleast one exit portion positioned in the web support surface, each exitportion being in continuous fluid communication with a region externalof and immediately adjacent to the web support surface; a source ofpressurized gas in fluid communication with the passages; a coatingdeposition station positioned adjacent the web support surface; and aset of seals positioned near the web support surface, said set of sealsforming a sealed region extending over an arc of the drum angularlyspaced from the coating deposition station as the drum rotates relativeto the set of seals, said set of seals operative to substantiallyprevent pressurized gas from escaping from the exit portions in thesealed region to a coating region adjacent the coating depositionstation; said exit portions cyclically moving through the sealed regionand the coating region as the drum rotates.
 2. The invention of claim 1further comprising: first and second winding hubs rotatably mountedadjacent the drum; a web wrapped around the hubs and wrapped partiallyaround the drum on the web support surface in the coating region, saidweb spaced from the web support surface over at least a major part ofthe sealed region.
 3. The invention of claim 1 wherein each seal sealsagainst the web support surface.
 4. The invention of claim 2 whereineach seal seals against the web.
 5. The invention of claim 3 furthercomprising a manifold in fluid communication with the source ofpressurized gas, wherein each seal is coupled with the manifold to sealthe manifold to the web support surface, and wherein the manifoldconducts pressurized gas from the source into the passages via the exitportions in the sealed region.
 6. The invention of claim 1 wherein eachpassage comprises an elongated passage extending circumferentiallyaround the drum and in fluid communication with at least one of the exitportions.
 7. The invention of claim 1 wherein each passage comprises anelongated portion extending axially along the drum and in fluidcommunication with at least one of the exit portions.
 8. The inventionof claim 1 wherein the exit portions comprise elongated slits.
 9. Theinvention of claim 1 wherein the exit portions comprise tubes.
 10. Theinvention of claim 1 wherein the deposition station comprises multipledeposition sources.
 11. The invention of claim 1 wherein the source ofpressurized gas comprises a gas pressure regulation system.
 12. Theinvention of claim 5 wherein each passage comprises an elongated passageextending circumferentially around the drum and in fluid communicationwith at least one of the exit portions.
 13. The invention of claim 12wherein the manifold and the elongated passages extend over a workingaxial width of the drum such that pressurized gas at a substantiallyuniform, elevated pressure is introduced between the web and the websupport surface across the working axial width of the drum.
 14. Theinvention of claim 3 further comprising a plurality of manifolds, eachmanifold in fluid communication with the source of pressurized gas at arespective pressure, wherein each seal is coupled with the manifolds toseal the manifolds to the web support surface, and wherein each manifoldconducts pressurized gas at the respective pressure into respective onesof the passages via the respective exit portions in the sealed region.15. A method for coating a web in a web coating process, said methodcomprising: (a) providing a coating deposition station and a rotatabledrum, said drum comprising a web support surface and a plurality ofpassages, each passage comprising at least one exit portion positionedin the web support surface, each exit portion being in continuous fluidcommunication with a region external of and immediately adjacent to theweb support surface; (b) transporting a web pressed against the websupport surface past the coating deposition station; (c) supplying apressurized gas via the passages and the exit portions into a regionbetween the web and the web support surface, thereby improving thermalcontact of the web with the drum; and (d) sealing the exit portions notcovered with the web with at least one seal that seals against the websupport surface as the drum rotates relative to the seal.